Generally, service providers of packet communications charge for packet services by measured rates corresponding to packet information amounts rather than by communication time periods corresponding to connection duration.
This is because to achieve the measured rate system, it is enough for each packet switching node of the network only to write, when starting each packet service, a table for determining a route toward a destination in accordance with a packet destination address, and no other processings are required until the next packet with that destination address arrives. Thus, the measured rate system is economically viable for the service providers.
On the other hand, having established a transmission route once at the beginning of a packet communication, its user is not charged unless he or she actually transmits a packet. Thus, the user usually holds the packet line for making intermittent low information rate communications, which provides an advantage of being able to transmit and receive a packet immediately when information takes place, without setting up communications each time for exchanging information.
Holding the packet line, however, occupies a part of the resources of the packet network, such as resources for maintaining transmission quality. The resources in the network occupied for setting up packet lines are not charged.
If the resources in the network is unavailable (this is referred to as "busy"), another user who tries to establish a communication afterward cannot achieve this. To provide the packet communications services simultaneously for a great number of (unspecified) users making use of the resources of a particular section in common, the resources in that section must be prepared for individual users, requiring an enormous amount of resources. This not only imposes heavy economic burden on the carrier, but also involves a waste of the resources during such hours as midnight when they are not used enough.
Furthermore, besides the packet transmission processings described above, the packet communication services in the mobile communications require mobility control because of roaming of users. In other words, handover is required which switches, following the roaming of a mobile station, base stations that communicate with the mobile station. Accordingly, when providing the packet communications services in the mobile communications, it is desirable to earn its cost that rates by amounts of roaming be added to the measured rates. Most users, however, are unacceptable such a rate system that differs from that of the services widely provided in fixed networks.